Weather resistance and heat aging characteristics of vulcanized conjugated diene rubbers such as natural rubbers (NR), isoprene rubbers (IR), styrene-butadiene rubbers (SBR) and butadiene rubbers are poor. Therefore various attempts to improve the weather resistance and heat aging characteristics of vulcanized conjugated diene rubbers are well known in the art by blending an ethylene-alpha-olefin copolymer rubber (EPDM) which is excellent in weather resistance and heat aging characteristics, with a conjugated diene rubber and vulcanizing the resulting blend. However, there has been involved such a problem that mutual vulcanization of the conjugated diene rubber and the EPDM becomes insufficient because of a slow vulcanization rate of the latter, thereby causing the mechanical strength of the resulting vulcanized rubber become poor.
It has now been found by the present inventors that a blend comprising the conjugated diene rubber, EPDM and a styrene oligomer, can provide a vulcanized rubber having satisfactory mechanical strength without reducing weather resistance and heat aging characteristics. The invention is based on this finding.
An object of the invention is to solve the above-mentioned problem associated with the prior art and another object of the invention is to provide a vulcanizable rubber composition capable of providing a vulcanized rubber which is excellent not only in weather resistance and heat aging characteristics, but also in mechanical strength. Still another object of the invention is to provide a vulcanized rubber which is obtained from the above-mentioned composition and which is excellent not only in weather resistance and heat aging characteristics but also in mechanical strength.